The invention relates to an electronic watch in which the "seconds" indication of the watch is automatically corrected by detecting a time announcement given by a radio or television receiver, and more particularly, to such arrangement where an audio signal from a receiver is fed to a band pass filter to derive a signal of a frequency which corresponds to a time announcement signal comprising a burst of signals and in which the duration of and the time interval between the filtered signals is determined in a digital manner by a time announcement pattern discriminator using a reference clock in order to decide whether the received signal represents a desired time announcement signal, the "seconds" indication of a watch being automatically corrected in accordance with the time announcement by utilizing a 30 seconds over-center reset circuit whenever the signal is determined to be a regular time announcement signal.
An electronic watch which utilizes a quartz oscillator as an oscillator source has a high level of frequency stability in providing a reference oscillation signal. A time error is within .+-.5 to 15 seconds per month, and hence a correct time indication can be maintained if the "seconds" indication is corrected at least once per month. However, with conventional electronic watches, a reset operation of "seconds" indication or the start of running after the time modification takes place by a manual operation of a button switch of the watch in timed relationship with a time announcement which is produced by a radio or television receiver. This manual operation is cumbersome and may cause a mistaken timing adjustment very frequently.
While there is a proposal for the provision of an electronic watch in which a time modification is automatically performed by detecting a time announcement from a radio or television receiver, it remains to be theoretical only, and involves practical difficulties. These difficulties are caused by the fact that a microphone must be used to pick up a time announcement signal, but may also pick up environmental noises or ticking sound of the watch itself. In order to determine if the signal picked up represents a time announcement signal, the entire pattern of the time announcement signal must be recognized. There has been available no discrimination circuit which exhibits a good immunity from noises and assures a reliable detection of a time announcement pattern and which is suitable to be incorporated into an electronic watch. The discrimination, if possible at all, is limited to a single time announcement pattern, and is not amenable to a generalized use.